This invention relates to asphalt recycling, and more particularly to an apparatus which heats and dries nuggets of asphalt which have been ripped from a paved surface to convert them into asphalt which can be used in the same manner as newly manufactured asphalt.
Asphalt and Portland Cement (concrete) are the two constituents of hard surfacing for the major roads in America's transportation system. In excess of 90% of America's roads are surfaced with asphalt. Asphalt is typically manufactured in large scale plants by mixing sized aggregate, sand, and asphalt cement (petroleum compound). This mixture is then dispensed into transport vehicles and taken to jobsites. Most current asphalt jobs involve re-paving existing roadways or parking areas, which often requires the old pavement to be transported away from the jobsite after it is ripped from the paved surface.
As an alternative to manufacturing new asphalt in an asphalt plant, chunks or nuggets of discarded asphalt can be recycled and reused as asphalt. The waste asphalt nuggets can be re-introduced into new asphalt mixtures, or they can be reheated and used for patching paved surfaces. If properly prepared, recycled asphalt can be of the same quality as new asphalt, yet it is cheaper to produce. Recycling of asphalt can be done on a large scale in an asphalt plant, or on a smaller scale using recycling machines at the jobsite.
U.S. Pat. Nos. 5,791,814 and 4,946,307 disclose an apparatus for recycling asphalt at a job site. Although on-site recycling devices have limited production compared with large asphalt plants, the on-site application increases time and cost efficiency because the asphalt does not need to be transported to and from the asphalt plant. By using the asphalt recycling machines, contractors can avoid buying new fresh mix from an asphalt plant, trucking costs to get the fresh mix to the site and the old asphalt to a disposal area, and, in some cases, dumping fees.
Output quality and quantity from asphalt recycling machines varies depending on the condition of the asphalt being recycled, its moisture content, and the amount of contamination (non-asphaltic material) contained in the asphalt. To achieve high quality and quantity of recycled asphalt, the reusable nuggets of asphalt must be warm and dry before they are introduced for recycling. The use of warm, dry asphalt increases both the physical strength and the adhesion strength of the recycled product. U.S. Pat. No. 5,335,989 describes an enclosed heated chamber called a “hotbox” which is used to heat and dry asphalt nuggets before they are introduced for recycling. After several hours in a hotbox, the reusable nuggets of pavement are soft, warm, dry, and capable of being manually shoveled into potholes or introduced for recycling. One problem with hotboxes is that they do not allow continuous introduction of waste asphalt, rather, for each batch of asphalt, the chamber must be filled, sealed, heated, and emptied. Another problem with hotboxes is that large nuggets of asphalt must be manually broken before or during application. Another problem with hotboxes is that they have no means for homogenizing or mixing the material while it is in the hotbox. This lack of mixing reduces quality and quantity of recycled product because it produces some asphalt that is too hot, and some asphalt that is too cold. Furthermore, many hotboxes require waste asphalt to be shoveled into and out of the heating chamber, which requires excessive amounts of time and labor.
Some on-site asphalt recycling machines comprise drying chambers that allow the waste asphalt to be dried in the recycling machine before the recycling process begins. However, this drying step is usually the rate determining step for the entire process. Furthermore, the drying chambers in the recycling machines have many of the same problems as the hotboxes discussed above, such as “batch” loading, and the lack of a mixing means.
Therefore, it is an object of the present invention to provide a device which efficiently heats and dries nuggets of asphalt ripped from a paved surface.
It is further an object of the invention to provide a device that allows for continuous loading and unloading of asphalt instead of batch loading.
It is further an object of the invention to provide a device that is capable of on-site applications so that waste asphalt can be recycled and reused at the jobsite.
It is further an object of the invention to provide an efficient device for use in asphalt recycling which will make asphalt recycling cost effective for contractors and thus reduce the amount of waste asphalt sent to landfills.
Other objects of the present invention will be apparent from this specification.